1. Field of the Invention
The present invention relates to a carburetor for a general purpose internal combustion engine, and, more particularly, to a carburetor for a general purpose engine which is prominent in restarting he engine at high temperatures.
2. Description of the Related Art
In recent days of automobiles, in order for automobile engines to achieve fulfillment of regulations on emissions or a strong demand for lowering levels of emissions, it has been employed to burn a fuel mixture as lean as possible. On these grounds, the temperature of fuel combustion is set rather on the higher side for the lean burn internal combustion engine as compared to the conventional internal combustion engines. A soundproofing type of automobile engine that is surrounded by a sound insulation wall to lower a level of sound is lacking in heat dissipation capacity in a constructional point of view, which makes it hardly avoidable that the engine remains hot for a relatively long period of time after an engine stop.
On the other hand, a carburetor, that is used to mix fuel and air in correct proportions, generally has an aluminum die-cast barrel body. The carburetor barrel body is formed with various bores used as passageways including fuel passages and bleed air passages which form part of carburetor circuits for performing specific functions. Almost of all of the passages are drilled excepting bores formed by the use of pin extraction. The carburetor barrel body is a die-cast product of aluminum, an excellent heat conductive material, is connected to an intake manifold of the engine, and is heated by a high combustion temperature of the engine and easily gets a high temperature as a whole and, in consequence, in particular in the case where the carburetor is installed to the sound proofing type of engine, remains at a high temperature for a long period of time after an engine stop. In this condition, fuel in a fuel well of a main fuel supply passage (main carburetor circuit) evaporates in a period of engine stop. The engine is possibly forced to restart without supply of fuel into an air passage, namely, an air horn, in particular, in the case where the carburetor is equipped with means for closing a fuel inlet port when the engine stops as a countermeasure to dieseling or running-on, which is a condition in which an engine continues to run after the ignition key is turned off. Furthermore, when restarting the engine at high temperatures, fuel evaporates as soon as it is introduced into the fuel well, which is always one of various causes for difficulties in high temperature engine starting. One of some typical countermeasures against the difficulty is installation of a heat insulation gasket between the carburetor barrel body and the intake manifold. Another countermeasure is to construct a carburetor made up of a carburetor barrel body formed with fuel and air passages and a fuel bowl (fuel container) for providing a constant level fuel chamber therein which are made of high heat conductive materials such as known from, for example, Japanese Utility Model Publication No. 49-39710.
Although heat insulation gaskets are effective in the insulation of heat that is transferred to the carburetor barrel body from the engine through the intake manifold, they are incapable of preventing the carburetor barrel body from direct exposure to high temperature heat radiation heat from, in particular, the soundproofing type engine, so as to have no effect of reducing the difficulty of high temperature restarting. The carburetor that is made up of synthetic resin molding products, namely, a synthetic resin molding carburetor barrel body and a synthetic resin molding fuel bowl, has no presence of cavities which, on one hand, allows an extremely close arrangement of the air and fuel passages to one another without a possible occurrence of accidental communication between the passages and, on the other hand, causes aggravation of mechanical strength of the carburetor, so as to bring about not only the necessity of a reinforcement for the carburetor for installation to the intake manifold without an occurrence of deformation and/or damage, but also the difficulty of firmly and steadily mounting functional parts generally made of metal such as a throttle valve and jets to the carburetor.
Many of the air and fuel passages and bleed air passages that are formed in the metal carburetor barrel body or the synthetic carburetor barrel body usually have bent sections. Such passages are formed by drilling the carburetor barrel body from various sides and are then plugged at one end with stoppers such as a ball plug, respectively, which is always undesirable in light of preventing or significantly lowering the number of working man-hours, the number of parts and possibilities of leakage of fuel and/or air. Furthermore, the carburetor barrel body, which is an aluminum die-cast product, has a considerably complicated mechanical structure, so as to often yield cavities distributed in the cast, which are commonly called xe2x80x9cblow holesxe2x80x9d. In consequence, the air and fuel passages that are drilled and arranged extremely close to one another in the carburetor barrel body are accidentally interconnected to one another through the cavities. Especially, carburetors for use with general purpose engines are small in size and typically employ horizontal air horns. In such a carburetor that is made up of a carburetor barrel body formed with a horizontal air horn, a fuel bowl secured to the carburetor barrel body, and a column-shaped fuel trunk formed with fuel passages therein which is installed between the carburetor barrel body and fuel bowl so as to extend along a vertical center line from the carburetor body, there are quite a lot of chances of an occurrence of accidental interconnection between the fuel passages through cavities due to an extremely close arrangement, which leads to one of the causes of a decline in yield rate of finished carburetors. Such a passage is formed by drilling the carburetor barrel body from various sides and is then plugged at one end with a stopper such as a ball plug, which is always undesirable in light of preventing or significantly lowering the number of working man-hours, the number of parts and possibilities of leakage of fuel and/or air.
It is an object of the present invention to provide a carburetor for, in particular, a general purpose internal combustion engine, which improves the issue that a metal die-cast carburetor barrel body is one of the problems of high temperature restarting of the engine.
It is another object of the present invention to provide a carburetor which overcomes the problem that a synthetic resin carburetor barrel body is employed with the intention to overcome the issue that a metal die cast carburetor barrel body is one of the problems of high temperature restarting of the engine, and in other words, the issue that a carburetor with a synthetic resin carburetor barrel body incorporated therein is lacking in mechanical strength.
It is another object of the present invention to provide a carburetor having a structure that realizes assembling performance of functional parts relating to the carburetor.
It is still another object of the present invention to provide a carburetor in which it is relatively easy to form fuel and/or air passages.
It is a further object of the present invention to provide a carburetor which has a structure that prevents or significantly reduces the possibility of interconnection between fuel and/or air passages and fuel leakage.
According to one aspect of the present invention, in a carburetor which comprises a carburetor barrel body having a horizontal air passages, a fuel bowl secured to the bottom of the carburetor barrel body, a column-shaped fuel trunk disposed between the fuel tank and carburetor barrel body so as to extend from and align with a vertical center line of the carburetor barrel body, and fuel passage means disposed partly in the carburetor barrel body and partly in the column-shaped fuel trunk for delivering fuel into the horizontal air passages, significant improvement is achieved by providing the carburetor barrel body and the column-shaped fuel trunk separately by forming them from different materials, namely a metal and a synthetic resin, respectively, and forming fuel wells in the column-shaped fuel trunk. The carburetor structure in which the column-shaped fuel trunk with the fuel wells formed therein is made of synthetic resin that is lower in heat conductivity than metals and is half dipped in liquid fuel in the fuel chamber in practical use prevents or significantly reduces transfer of high temperature heat from the engine after an engine stop, so as to allow only a small quantity of fuel to evaporate from the fuel wells or to restrain evaporation of liquid fuel introduced into the fuel well at an engine restart even if a large quantity of fuel has evaporated from the fuel wells, ensuring an easy restarting of the engine that remains still hot. The carburetor barrel body that is connected to an intake manifold is made of metal, and has a sufficient mechanical strength for steady installation of functional parts such as throttle valve and a choke thereto.
The carburetor structure in which each or both of a low speed fuel passage and a fuel supply passage are formed partly in the shape of groove in an interface between the carburetor barrel body and the column-shaped fuel trunk yields a significant reduction in man-hours for drilling the carburetor barrel body from various sides and the column-shaped fuel trunk to form bores for passages, and also eliminates, in combination with utilization of synthetic resin for the column-shaped fuel trunk, the possibility of interconnection of the passages arranged close to one another in the column-shaped fuel trunk. That is to say, because the carburetor barrel body formed with the intake passage and the column-shaped fuel formed with the wells are separately made of metal and synthetic resin, respectively, the carburetor yields high temperature engine start ability without loosing necessary mechanical strength and realizes formation of the fuel passages and air bleed passages that is free from air and/or fuel leakage with a reduced number of working man-hours by utilization of the interface between the carburetor barrel body and column-shaped fuel trunk.
According to another aspect of the present invention, in a carburetor which comprises a carburetor barrel body made of metal having a horizontal air passage extending transversely therethrough, a fuel container forming a constant level fuel chamber therein and coupled to a bottom the carburetor barrel body, a column-shaped fuel trunk formed with fuel wells which is made of synthetic resin separately from the carburetor barrel body and disposed between the carburetor barrel body and the fuel container so as to extend from and align with a vertical center line of the carburetor barrel body, and fuel passage means disposed partly in the carburetor barrel body and partly in the column-shaped fuel trunk for delivering fuel into the horizontal air passage, significant improvement is achieved by providing the column-shaped fuel trunk with an integral top flange and installing the column-shaped fuel trunk between the carburetor barrel body and the fuel container so as to extend from the carburetor barrel body into the fuel container by bolting the fuel container to the carburetor barrel body in positions outside of the mounting flange of the column-shaped fuel trunk with the top flange of the column-shaped fuel trunk put in a tight contact condition between the fuel container and the carburetor barrel body so as thereby to provide a tight interface between the carburetor barrel body and the top flange of the column-shaped fuel trunk. The carburetor thus structured exerts a coupling force on the top flange of the column-shaped fuel trunk and the column-shaped fuel trunk itself at the center of the top flange indirectly through the fuel container, as a result of which the column-shaped fuel trunk is prevented from deformation or damage due to strong direct compressive stress and receives a uniform load over the entire surface area of the top flange thereof with an effect of providing a watertight and airtight interface between the carburetor barrel body and the top flange of the column-shaped fuel trunk, so as thereby to prevent the fuel passage from fuel leakage at the interface. The carburetor may further comprise sealing means for sealing an outer periphery of the interface and the fuel passage in the interface with an effect of providing more reliable water-tightness and air-tightness.
The fuel passage means may include the low speed fuel passage and/or fuel supply passage being partly defined as grooves in the interface. In this instance, the sealing means is configured so as to seal, in addition to the outer periphery of the interface and the main fuel passage in the interface, the groove-shaped passage sections. Utilization is made of the interface between the carburetor barrel body and the flange of the column-shaped fuel trunk for the grooves which are used as parts of the fuel passages, which yields a significant reduction in man-hours for drilling the carburetor barrel body from various sides and also eliminates, in combination with utilization of the sealing means and utilization of synthetic resin for the column-shaped fuel trunk in which the fuel passages are formed close to one another, the possibility of interconnection of the passages and leakage of fuel from the passages, which leads to significantly increased reliability of the carburetor. That is to say, because the carburetor thus structured exerts a coupling force on the top flange of the column-shaped fuel trunk and the column-shaped fuel trunk itself indirectly through the fuel container, the column-shaped fuel trunk with its top flange, which is delicate in mechanical strength, is prevented from deformation and/or damage, so that the carburetor barrel body and the flange of the column-shaped fuel trunk can be tightly contacted with a force sufficiently strong as to prevent leakage of fuel and/or air through the interface therebetween. Furthermore, utilization of the interface for the grooves which are used as parts of the fuel and air passages yields a significant reduction in man-hours for forming the fuel and air passages in the carburetor barrel body, and utilization of the sealing means between the carburetor barrel body and the flange of the column-shaped fuel trunk provides the passage means with high water-tightness and air-tightness with an effect of eliminating fuel and/or air leakage.